Bird Diversity Decreases Spread of West Nile Virus

Guest Author - Malika Harricharan

A study by biologists at Washington University in St. Louis shows that the more diverse a bird population is in an area, the less chance humans have of exposure to West Nile Virus. Whohoo! Let's hear it for the birds.

Some bird species a good transmitters of the virus while others aren't. The idea behind the study is that when there are more bird species in an area, there is less likely opportunity of the West Nile Virus spreading as their are a fewer number of what would be considered good hosts. This, in turn, lowers the risk for humans.

Some bird species that are good transmitters are house finches, blue jays, sparrows, crows and Robins. Robins are the most prolific carrier of the West Nile Virus. This is probably because they feed so much on the ground so it is easy for mosquitoes to bite them. The areas where the incidence of West Nile Virus reservoirs is high tend to occur in urban and suburban areas. This is where diversity is low.

Although the diversity of birds is very important, it is not the sole factor affecting the spread of West Nile Virus. It also has to do with the proportion of birds. Researches say that you must have not only a diverse group of species, but the proportions of the species need to be divided out evenly as well. So, for example if you have 100 animals, and 5 species, the optimum should be 20 of each species. Researchers have found that in urban and suburban areas the proportions are more like 90 of one species.

The study has been thoroughly researched. It began five years ago, when the West Nile Virus was just beginning to receive much attention. The researchers identified many field sites, both urban and rural. This includes an area just outside of St. Louis comprised of 2000 acres.

The set up mosquito traps and studied different mosquito species. The Centers for Disease Control provided kits to test the mosquitoes for West Nile Virus. Using these kits they were able to find three positive pools.

The found the infection rates to quite low. It was something like 1 in 1000 carrying the West Nile Virus. Once they proved this in their test area, they expanded the study to include a wider area to make sure that this was not just an isolated incident or coincidence. Other areas in St. Louis and the surrounding areas supported these facts as well. The greater the diversity of bird species the lower the incidence of West Nile. And the less the diversity the greater chance of the West Nile.

To broaden the study to include the United States, the researchers gathered data on human cases of the West Nile Virus and compared these with the diversity of bird populations across the US. Once again, their findings were supported.

This is good news for bird conservation. The fact that actually helping to encourage diversity could help one's health is a huge motivating factor.